1. Field of the Invention
The present invention relates to a color electroluminescence display element, and more particularly to a color electroluminescence display element and the manufacturing method thereof which are capable of improving a RC-time delay phenomenon caused by a high resistance of a transparent electrode and the contrast of the electroluminescence display element.
2. Description of the Prior Art
Several kinds of flat display elements have been known: a liquid crystal display (LCD) element, a plasma display (PDP) element, an electroluminescence (EL) display element, and so forth. To carry out a high-density image display, the above elements should be completely colorized, and thus a number of studies therefor have been progressing so far. Among the elements have the LCD and the PDP now been completely colourized. Meanwhile, there has been great amounts of research for the development of an EL display element wherein a white light is produced and filtered for display with complete colors.
FIG. 1 is a cross-sectional view of a conventional EL display element utilizing the white light as mentioned above. According to the EL display element of FIG. 1, a metal electrode 2 is formed by vacuum-evaporating a metal such as aluminium on a glass substrate 1 with a thickness of about 2000 .ANG., and then by line-etching the formed metal utilizing photoetching technique. A first insulating layer 3 is formed by seating a dielectric material, such as SiON, BaTa.sub.2 O.sub.6, SrTIO.sub.3, etc., on the metal electrode 2 with a thickness of about 3000 .ANG. by means of sputtering. A light-emitting layer 4 is formed by forming a fluorescent material for emitting a white light, such as SrS; Ce, Eu, X, ZnS; Pr, ZnS; Mn/SrS; Ce/ZnS; Mn, etc., on the first insulating layer 3 with a thickness of 0.5 to 1.5 .mu.m by means of vacuum evaporation, multi-source deposition, etc. A second insulating layer 5 is formed by forming SiON, BaTa.sub.2 O.sub.6, SrTIO.sub.3, or the like on the light-emitting layer 4 with a thickness of about 3000 .ANG. by means of sputtering. A transparent electrode 6 is formed by forming a transparent film layer of indium tin oxide(ITC) on the second insulating layer 5 with a thickness of about 2000 .ANG. and %hen by line-etching the transparent film layer in a perpendicular direction of the metal electrode 2 by means of photoetching. The panel manufactured by the above process is referred to as an EL panel 10.
In addition, on a transparent sealing plate 9, which is prepared for protecting the EL panel 10 from humidity, oxygen, or or the like, a color filter 8 is formed. The color filter 8 is arranged on the transparent sealing plate 9 so that red(R), green(G), and blue(B) color filters, which constitute %he color filter 8, are positioned in order. The widths of the R, G, and B color filters are the same as those of the metal electrode 2 and the transparent electrode 6, respectively. The transparent sealing plate 9 and the color filter 8 are sealed together with a thickness of several .mu.m. The panel manufactured by the above process is referred to as a filter panel 20.
The manufacture of the color EL display element is completed by injecting silicon oil 7 between the EL panel 10 and the filter panel 20.
In the conventional EL display element having the above construction, if an AC voltage of 200 V or so is applied between the metal electrode 2 and the transparent electrode 6, hot electrons are created by a strong electric field based on the applied AC voltage. The hot electrons collide with doped molecule centers in the light-emitting layer 4, such as cerium(Ce), praseodymium(Pr), manganese(Mn), etc., and excite electrons of the molecular centers from its valence band to its conduction band. The electrons excited into the conduction band are instable, and thus fall to the valence band with the emission of a natural light.
The light from the EL panel 10 according to the above process is a white light containing the wavelengths of R, G, and B color lights at a uniform rate. The white light is separately emitted by both the metal electrode 2 and the transparent electrode 6, and is filtered into the color lights of R, G, and B through the color filter 8. Thus, the combination of three filtered color lights makes it possible to express a colorific display.
However, since the conventional EL display element colorized by using the white light employs an aluminium-coated metal electrode, it has the disadvantage that a needless light reflected from the very surface of the aluminium to the user, and thus the quality of contrast deteriorates. Also, the distance between the color filter 8 and the light-emitting layer 4 is so distant %hat a phenomenon of parallax between each pixel may be caused. It has also the disadvantage that the RC-time delay may occur, when a wide-area EL display element for a VGA monitor or an HDTV, is driven, due to a high resistance of the transparent electrode,